1. Field of the Invention
The present invention relates to a vehicular transmission including a main shaft, a countershaft, gear trains, a shifter, and a shift drum. Specifically, the main shaft can receive power transmitted from an engine. The countershaft is connected to a drive wheel. The gear trains are disposed between the main shaft and the countershaft, allowing a plurality of gear positions to be selectively established. The shifter is disposed between idle gears, each forming part of two of the gear trains achieving the plurality of gear positions and supported rotatably on the main shaft or the countershaft, so as to be relatively unrotatable on, and to be slidable along, the main shaft and the countershaft. The shift drum includes lead grooves formed on an outer periphery thereof. A shift fork rotatably holding the shifter is engaged with the lead grooves. The shift drum is rotatable about an axis that extends in parallel with the main shaft and the countershaft. The transmission shuts down power transmission from the engine to the main shaft when the shifter is slidably moved between a first position, at which the shifter is engaged with one of the two idle gears and a second position, at which the shifter is engaged with the other of the two idle gears.
2. Description of Background Art
A known vehicular transmission, as disclosed in Japanese Patent Laid-open No. Hei 9-317881, includes a first gear train establishment portion, a second gear train establishment portion, and a lead groove. The first gear train establishment portion engages a shifter with one of a pair of idle gears. The second gear train establishment portion is disposed at a position offset axially along a shift drum from the first gear train establishment portion so as to engage the shifter with the other one of the pair of idle gears. The lead groove, disposed on an outer periphery of the shift drum, forms a communication portion connecting linearly the first and second gear train establishment portions.
In the vehicular transmission disclosed in Japanese Patent Laid-open No. Hei 9-317881, however, when the shifter is slidably moved to be disengaged from the one idle gear and engaged with the other idle gear, there is involved a relatively large difference in speed between the shifter and the idle gear to be engaged with therewith, resulting in a large engagement noise. This is particularly conspicuous in a vehicle arranged to select automatically a gear position according to an upshift or downshift operation and arranged to make a preliminary gearshift during running at a given gear position. Specifically, in such a vehicle, there is produced a large engagement noise that is not operatively associated with an operation performed by an occupant of the vehicle. This gives the occupant a sense of discomfort.
The present invention has been made to address the foregoing situation and it is an object of the present invention to provide a vehicular transmission that can suppress the engagement noise produced when the shifter is moved slidably to select a gear position.